A. Technical Field
The present invention relates to a (meth)acrylic copolymer and its production process, wherein the (meth)acrylic copolymer is, for example, used favorably for such as water-treating agents, scale inhibitors, anticorrosives, additives for excavation, soil-treating agents, dispersants, and detergent builders.
B. Background Art
Of water-soluble polymers such as (meth)acrylic (co)polymers, low-molecular-weight ones have hitherto been used favorably for such as dispersants (such as for inorganic pigments and metal ions), scale inhibitors, anticorrosives, or detergent builders by utilizing the excellent chelating ability and dispersibility of the low-molecular-weight water-soluble polymers.
There have hitherto been reported some arts to enhance the dispersibility, the scale inhibitability, and the anticorrosive ability by introducing phosphorus atoms into structures of the (meth)acrylic (co)polymers as follows.
There is reported a heat-resistant scale inhibitor including a (meth)acrylic polymer obtained by polymerizing (meth)acrylic acid in the presence of hypophosphorous acid (e.g. refer to JP-A-293599/1986).
There is reported an anticorrosive including a (meth)acrylic copolymer as an essential component wherein the (meth)acrylic copolymer is obtained by polymerizing a monomer mixture in the presence of hypophosphorous acid (salt) wherein the monomer mixture includes an unsaturated carboxylic monomer (e.g. (meth)acrylic acid) and a sulfonic-acid-group-and/or-hydroxy-group-containing unsaturated monomer (e.g. refer to JP-A-214186/1987).
There is reported a process for producing an anticorrosive for metals by polymerizing an unsaturated carboxylic monomer (e.g. (meth)acrylic acid) while gradually introducing hypophosphorous acid (salt) (e.g. refer to JP-A-163191/1991).
There is reported a process for producing a (meth)acrylic water-soluble polymer by carrying out polymerization while gradually introducing a (meth)acrylic water-soluble monomer, a polymerization initiator, and hypophosphorous acid (salt) into an aqueous medium, wherein the (meth)acrylic water-soluble polymer to be produced is excellent in the inorganic-pigment dispersibility, the scale inhibitability, and the anticorrosive ability (e.g. refer to JP-A-263803/1994).
Because the phosphorus-containing (meth)acrylic (co)polymers which have hitherto been reported as mentioned above are excellent in the dispersibility, the scale inhibitability, and the anticorrosive ability, they could be applied favorably to dispersants, scale inhibitors, and anticorrosives.
However, these prior phosphorus-containing (meth)acrylic (co)polymers have problems of: not sufficiently displaying the calcium-ion-binding ability which is one of important builder performances; and therefore being unusable as high-performance detergent builders.
In addition, (co)polymers to be used for such as dispersants, scale inhibitors, anticorrosives, and detergent builders are required to have a property of little gelling (gelation resistance). However, the prior phosphorus-containing (meth)acrylic (co)polymers are poor in the gelation resistance. For example, in the water system of high hardness in which the ion concentration in water is very high (e.g. in seawater), the prior phosphorus-containing (meth)acrylic (co)polymers are put under circumstances where they extremely easily gel.
A. Object of the Invention
Accordingly, an object of the present invention is to provide a (meth)acrylic copolymer and its production process, wherein the (meth)acrylic copolymer has the good chelating ability and dispersibility and is excellent both in the calcium-ion-binding ability and the gelation resistance in combination, and further, the deterioration of these various performances is inhibited even in the water system of high salt concentration.
B. Disclosure of the Invention
The present inventors diligently studied to solve the above problems. As a result, they have completed the present invention by finding out that all the above problems can be solved only in the case where, in a low-molecular-weight (meth)acrylic copolymer which comprises a constitutional unit derivative from a (meth)acrylic monomer and a constitutional unit derivative from a (meth)allyl-etheric monomer of a specific structure and has a phosphorus atom in the main chain, there exist the constitutional unit derivative from the (meth)acrylic monomer and the constitutional unit derivative from the (meth)allyl-etheric monomer of the specific structure in a specific ratio, and the phosphorus compound content is not higher than a predetermined ratio wherein the phosphorus compound is not bonded to the copolymer.
That is to say, a (meth)acrylic copolymer, according to the present invention, comprises a constitutional unit (a) derivative from a (meth)acrylic monomer (A) of a general formula (1) below and a constitutional unit (b1) derivative from a (meth)allyl-etheric monomer (B1) of a general formula (2) below and has a phosphorus atom in the main chain;
with the (meth)acrylic copolymer being characterized by having:
a mutual ratio between the constitutional unit (a) and the constitutional unit (b1) in the range of the constitutional unit (a) 80 to 96 mol % and the constitutional unit (b1) 4 to 20 mol %; and a weight-average molecular weight in the range of 500 to 4,000; and
a weight P1 of phosphorus atoms as bonded to the copolymer and a weight P2 of phosphorus atoms as not bonded to the copolymer satisfy a relationship of 0.9xe2x89xa6P1/(P1+P2)xe2x89xa61.0; and further
a gelation resistance of not more than 0.02 and a calcium-ion-binding ability of not less than 150 mgCaCO3/g;
wherein the general formula (1) is: 
(wherein: R1 denotes a hydrogen atom or a methyl group; and X denotes a hydrogen atom, a metal atom, an ammonium group, or an organic amine group); and
wherein the general formula (2) is: 
(wherein: R2 denotes a hydrogen atom or a methyl group; and each of Y and Z independently denotes a hydroxyl group or a sulfonic acid group (wherein the sulfonic acid group may be in the form of a monovalent metal salt, a divalent metal salt, an ammonium salt, or a salt of an organic amine group) wherein at least one of Y and Z is the sulfonic acid group).
A process for producing a (meth)acrylic copolymer, according to the present invention, comprises the step of carrying out a copolymerization reaction of monomer components in the presence of hypophosphorous acid (salt) and a polymerization initiator to thereby produce the (meth)acrylic copolymer having a phosphorus atom in the main chain, wherein the monomer components include a (meth)acrylic monomer (A) of a general formula (1) below;
with the process being characterized in that the hypophosphorous acid (salt) begins to be supplied into the polymerization system earlier than the polymerization initiator;
wherein the general formula (1) is: 
(wherein: R1 denotes a hydrogen atom or a methyl group; and X denotes a hydrogen atom, a metal atom, an ammonium group, or an organic amine group).
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.